This invention relates to a disc trimmer with two circularlike segmented condenser plates, which can be rotated relative to each other and between which is arranged a dielectric.
Such disc trimmers serve as a variable capacitor, whereby the maximum capacitance is reached when the condenser plates are arranged in a covering or overlapping fashion on top of each other, and the minimal capacitance corresponds with the turned position of the condenser plates.
In the known disc trimmers, the dielectric is formed as a layer which may, for instance, be circular and which covers the entire working area. Hereby significant initial capacitances develop even in the turned position of the condenser plates which are undesirable for many ranges of application. These initial capacitances depend on the final capacitances, which are to be achieved with the corresponding disc trimmer.
The invention has an objective to provide a disc trimmer in such a way that the initial capacitance is very low and virtually independent of the final capacitance.
This objective is achieved by a disc trimmer of the type mentioned initially in which the dielectric is approximately circular, corresponding with the shape of the plates and connected to one plate, approximately covering each other.
This arrangement eliminates the placing of a dielectric between the condenser plates even in the peripheral area in the initial or minimal position which would lead to a larger initial capacitance. At the same time, this makes the initial capacitance to a large extent independent of the final capacitance, since this is not or only minimally influenced by the thickness of the dielectric.
The invention further provides that the dielectric has an electrically conducting layer which serves as a plate. Such a layer can be applied to the dielectric, for instance, by evaporation or electrolytically. In this connection, ceramic can serve as the dielectric, while for instance silver can be used for the conducting layer.
It is advantageous if the coated dielectric is located in an opening of the supporting structure. Thus it is assured that even in very thin covering layers of the dielectric, for instance 0.1 mm, that the combination dielectric-condenser plate can be arranged and handled in the disc trimmer without the danger of mechanical damage. The connection between the dielectric and the supporting structure can be achieved by means of an adhesive.
It is of particular advantage if the surfaces of the dielectric and supporting structure facing the respective other plate are aligned. This can be achieved by grinding or polishing both together after having glued the dielectric to the supporting structure.
It is particularly favorable if the supporting structure is manufactured of synthetic material, which is unaffected by temperature changes and has a low dielectric constant such as a duroplast, e.g. an unsaturated polyester material. The low dielectric constant of the supporting structure also leads towards a possibly low initial capacitance and accordingly also towards an increased range of adjustment.
In the invention, the supporting structure is formed as a cylindrical rotor which receives an adjustment device.
Another embodiment of the invention provides that the supporting structure is formed as a stator carrying the rotor.
Other features which are considered characteristic of the invention are set forth in the appended claims.
Although the invention is illustrated and described in relationship to specific embodiments, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.